Selectively permeable zeolite adsorbents and sealants made therefrom

ABSTRACT

The invention relates to an improved adsorbent, essentially impermeable to oxygen and nitrogen but permeable to water vapor, and to sealants incorporating said adsorbent. The adsorbent comprises outgassed zeolite having pores with apertures large enough to permit entry of gases such as oxygen and nitrogen into the pore spaces and having on its surface, covering the pore apertures, a fluid which is essentially impermeable to nitrogen and oxygen molecules and yet permeable to water vapor. The zeolite adsorbent, and sealants prepared from the zeolite, are particularly useful in the fabrication of thermal insulating glazed windows having a sealed air pocket.

This application is a division of copending Application Ser. No.919,503, filed Oct. 16, 1986 now U.S. Pat. No. 4,745,711.

The present invention relates to an improved zeolite adsorbent. Thepresent invention also relates to sealants incorporating the improvedzeolite adsorbent. Such sealants have varied uses, one of which is inthe fabrication of thermally insulating multiple glazed structures suchas insulated glass.

BACKGROUND OF THE INVENTION

Zeolites are well known adsorbents, which have been used between glasspanes, either alone or in a sealant. The zeolite is disposed along theperiphery of the space enclosed by the panes, and the zeolite adsorbswater vapor from the space between the panes. Zeolite functions as a"molecular sieve". Specifically, zeolite has pores into which thematerial being adsorbed passes. The pores have apertures of a sizesufficient to pass the molecules of the material being adsorbed butsmall enough to block materials not adsorbed. U.S. Pat. Nos. 4,151,690,4,141,186 and 4,144,196 disclose such molecular sieve zeolites.

Known zeolites have pore aperture sizes of 3 to 10 angstroms. However,zeolites with aperture sizes 4 angstroms or greater, when used in aninsulating window, adsorb gaseous components in the air space, such asoxygen and nitrogen, as well as the water vapor which is desired to beadsorbed. These zeolites then outgas the oxygen and nitrogen when thetemperature rises or the pressure lowers. These zeolites, when used in asealant between glass panes in a window, adsorb the oxygen and nitrogenwhen cooled (as during night) and then release the gases when the glassis heated (as during the day). This causes large pressure variations inthe enclosed air space, which can lead to problems with the windows suchas excessive deflection or inflection. This outgassing can also lead toa loss of adhesion between the glass panes and the sealant becauseagglomeration of the gases permits small bubbles to form which migrateto the adhesive interface.

U.S. Pat. Nos. 4,144,186 and 4,144,196 attempt to solve this problem byusing zeolite adsorbents with pore apertures of 3 angstroms or less insize so that oxygen and nitrogen molecules cannot enter into the pores,thus preventing the adsorption and the desorption of these gases. U.S.Pat. No. 4,151,690 contemplates the use of zeolite adsorbents withlarger pore aperture sizes, which have been pretreated by preadsorptionof a low molecular weight polar material to partially suppress theundesirable adsorption of the gases.

BRIEF SUMMARY OF THE INVENTION

An object of the present invention is to provide a molecular sievezeolite adsorbent which has pore apertures of 4 angstroms or greater insize and which is free of the problems associated with the constantadsorption and desorption of gases. This is effected by heating thezeolite to drive out (or "outgas") the nitrogen and oxygen in its pores,and allowing it to cool while surrounded and covered by a fluid coatingwhich is essentially impermeable to oxygen and nitrogen yet permitswater vapor to slowly pass therethrough into the pores of the zeolite.Thus, the coated zeolite has a greater capacity to adsorb water vapor,which is desired, but does not adsorb any significant amount of oxygenor nitrogen. Outgassing the zeolite also places less nitrogen and oxygeninto the system where the zeolite is being used as an adsorbent.

The molecular sieve zeolite is in a particulate form. The particles havea plurality of pores throughout, some pores being adjacent the surface.The pores adjacent the surface have apertures at the surface largeenough to permit entry of oxygen and nitrogen molecules as well asmolecules of water vapor. The fluid coating on the surface of thezeolite extends over and covers the pore apertures, but does notpenetrate the pores. The coating may be any fluid which will coat thezeolite particles without being adsorbed into the pores, which isrelatively permeable to water vapor, and which is essentiallyimpermeable to nitrogen and oxygen (has a low solubility). The fluidprovides a barrier blocking the entry of oxygen and nitrogen into thepores. However, any water vapor which comes in contact with the fluid,solvates in the fluid and is transmitted through the fluid, into thepores of the zeolite, at a slow transmission rate. The zeolite with thefluid coating in accordance with the present invention may be used as apart of a sealant composition which is used between the glass panels ofa double glazed window.

The sealant is made by first mixing the molecular sieve zeoliteparticles with the fluid which may preferably be paraffinic oil.Approximately equal parts by weight of zeolite powder and oil are mixedtogether to form a slurry. The percentage of oil must be high enough sothat the oil is the continuous phase. The slurry is slowly heated undermild agitation and is kept heated for a sufficient time to outgas mostof the oxygen and nitrogen that may have been trapped in the pores ofthe zeolite. The material is then cooled to room temperature. The fluidat room temperature is essentially impermeable to nitrogen and oxygenand prevents nitrogen and oxygen from reentering the pores of thezeolite.

Thereafter the zeolite particles with the coating thereon are mixed withother components of a sealant material, and the resulting material isthen extruded to form the desired sealant.

BRIEF DESCRIPTION OF THE DRAWING

Further features and advantages of the present invention will beapparent to those skilled in the art to which it relates from aconsideration of the following description of a preferred embodiment ofthe present invention made with reference to the accompanying drawing inwhich the FIGURE is a fragmentary perspective view with parts in sectionshowing a sealant embodying the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a zeolite adsorbent and sealantsprepared therefrom useful for various purposes and especially useful forstructural sealants used in the fabrication of thermal insulatingmultiple glazed windows.

Zeolite is a known material which has the characteristic of being anexcellent adsorbent. Zeolite is available commercially from variouscompanies, including Union Carbide, W.R. Grace Company, and others. Thezeolite as used in the present invention is in a particle form, of amesh size of less than 100. The zeolite particles have a large number ofpores on the surface and throughout the mass of the zeolite. The poresare of a given diameter, slightly below the surface of the zeolite, witha smaller pore aperture extending through the surface. Zeolite which isusable for dessicating insulating glass units is available with poreaperture sizes ranging from 3 angstroms to 10 angstroms.

When zeolite is used as an adsorbent, it functions by drawing moleculesof whatever material is to be adsorbed, such as gas or water vapor,through the apertures of the pores and into the pores themselves, wherethe molecules are retained. Although the interaction of the zeolite withthe gas and vapor molecules is not fully understood, it is believed thatthere is an electrical charge on the zeolite material, and a charge ofopposite polarity on the molecules of the material being adsorbed, thuscausing an attraction of the molecules into the pores of the zeolite.

Because zeolite can be used as an adsorbent for different types ofmaterials, and these materials may have molecules of different sizes,the particular zeolite to be used in any particular application musthave pore apertures of a size large enough to permit passage of themolecules of the particular material to be adsorbed.

One known use for zeolite adsorbents is to function as a desiccant todraw water vapor out of the air space between two panes of glass in adouble glazed window. In this case, the zeolite must have pore apertureslarge enough to admit molecules of water vapor. As discussed above,however, it is desirable that the zeolite not adsorb molecules ofnitrogen and oxygen, the main gaseous components of air, from the airenclosed within the double glazed window. Zeolites having pore aperturesof 4 angstroms or greater in size will not exclude molecules of nitrogenand oxygen.

In order to provide a zeolite adsorbent which functions as thus desired,the present invention contemplates the use of zeolite which, although ithas pore apertures which are 4 angstroms or greater in size and thus arelarge enough to admit nitrogen and oxygen molecules, will not do sobecause there is a layer of gas impermeable fluid on the zeolite,extending across and covering the pore apertures on the surface of thezeolite. The fluid is, however, able to pass water vapor molecules.Therefore, the desired characteristics of both passage of water vaporand exclusion of nitrogen and oxygen are provided.

The fluid used in the present invention must have the followingcharacteristics. First, it must be able to coat zeolite particleswithout being adsorbed into the pores when properly mixed with thezeolite material. Second, it must be permeable to water vapor,preferably at a very low rate. Third, it must be essentially impermeableto nitrogen and oxygen, which are the main gaseous components of air.Many fluids may be useful in the present invention. These includeparaffinic oils, naphthenic oils, and aromatic oils; phthalates such asbutyl benzyl phthalate; polymeric polyesters such as Santicizer #278from Monsanto; polybutene; rubber process oils; and silicone fluids.

One fluid which has been successfully used in preparing the improvedzeolites of the present invention is Sun Par #2280, a refined petroleumproduct available from Sun Oil Co. This oil has a composition of 73%paraffinic carbon atoms, 23% naphthenic carbon atoms, and 4% aromaticcarbon atoms.

Although it will be appreciated that various methods of preparing thezeolite of the present invention are feasible, the following isillustrative of the preparation of the zeolite having the ability toadsorb moisture while not adsorbing nitrogen, oxygen and other gases.

A 4-angstrom molecular sieve zeolite (95 parts by weight) and a10-angstrom molecular sieve zeolite (95 parts by weight) were combinedwith 206 parts by weight of Sun Par #2280 and mixed for five minutes toinsure a uniform slurry or dispersion of the ingredients. The percentageof zeolite used must be low enough so that the fluid is the continuousphase. Any lesser amount of zeolite may be used if desired. The slurrywas slowly heated for about 15 minutes to a temperature of about 325° F.under mild agitation. The mixture was maintained at 325° F. for anadditional 30 minutes and then cooled to room temperature. The heatingcan also be performed under a vacuum, in which case a lower temperaturecan be used and the same results obtained.

The heating causes oxygen and nitrogen to be outgassed or removed fromthe zeolite. When the slurry is cooled the oil prevents the oxygen andnitrogen from reentering the zeolite. During the heating process, somewater vapor in the zeolite is also driven out, and no significant amountimmediately reenters the zeolite because the pore apertures of thezeolite are covered with the layer of fluid which has a very slowmoisture vapor transmission rate.

Although only one zeolite material may be used, it is often preferred touse a mixture of two or more zeolites. For example, equal parts byweight of a first zeolite having a pore aperture size of about 4angstroms, and a second zeolite having a pore aperture size of about 10angstroms, are used together. This use of two or more zeolites havingdifferent pore aperture sizes is sometimes preferred because there maybe present some large diameter impurities such as low molecular weightpolymer fractions, which can detract from the sealant's performancebecause of their volatility. These are adsorbed by large pore sizemolecular sieves.

In use, the zeolite adsorbent allows the controlled passage of watervapor. The water vapor penetrates or solvates in the fluid and passesthrough the fluid and into the zeolite pores. The nitrogen and oxygen,however, cannot significantly pass through the fluid and are therebyexcluded from entering the zeolite pores. Thus, there is very littleadsorption of gases into the coated zeolites.

As mentioned above, one preferred use of this improved zeolite adsorbentis in multipaned insulating windows. When a thermally insulated windowis constructed using two or more panes of glass sealed at the edges, anair space is created between the panes of glass. This air space willcontain air at ambient pressure. The air, of course, contains suchcomponents as nitrogen, oxygen and water vapor. In such a window, it isdesirable to remove the water vapor from the air between the panes ofglass, in order to prevent condensation of the water vapor on the glass.

For this use, the improved zeolite of the present invention may be usedalone as a dessicant or it may be incorporated into the sealant materialwhich is used at the edge of the window to seal between the panes ofglass. When the zeolite is mixed with the other ingredients of thesealant material while the sealant is being manufactured, it becomesdisposed within the matrix of the sealant material in such a manner asto be able to adequately function as an adsorbent for the air within thewindow. The air, of course, contacts the exposed surface of the sealant,and the water vapor is adsorbed from the air at that location.

FIG. 1 illustrates a composite structure A comprising a first member 10and second member 12 having facing, generally parallel surfaces, spaceda finite distance from each other. The composite structure A alsoincludes means for maintaining members 10, 12 in the spaced relationshipand for effecting a seal between the facing surfaces thereof.Specifically, a sealant and spacer strip, designated generally as 14,maintains the members 10, 12 in spaced relationship and provides theseal.

Members 10, 12 as illustrated are formed of glass, and the compositestructure A is a double glazed insulating glass window. However, it willbe appreciated that the invention has applicability in the environmentof an unrestricted variety of constructions and/or structural materials,including without limitation plastics and other materials.

The sealant and spacer strip 14 comprises an elongated ribbon 16 ofdeformable sealant, enveloping and having embedded therein a spacermeans 18 which extend longitudinally of ribbon 16. The spacer means 18is an undulating sheet of relatively rigid material which mayconveniently be formed of aluminum. It will be noted that all of thesurfaces and edges of the spacer means 18 are in intimate contact withribbon 16 of sealant. Such a spacer strip is shown in U.S. Pat. No.4,431,691. The sealant 16 includes the improved zeolite of the presentinvention.

There are many types of sealants usable in such windows, and many waysof preparing such sealants. Examples may be found in U.S. Pat. Nos.3,791,910 and 3,832,254.

A typical range of ingredients for a sealant is as follows:

400 to 600 parts butyl;

150 to 350 parts hydrocarbon resin;

10 to 15 parts zinc oxide;

100 parts carbon black;

100 parts aromatic resin; and

5 to 6 parts silane.

The fluid used in forming the slurry of zeolite and fluid, as describedabove, is also an ingredient of the sealant formulation, and functionsas a plasticizer. The amount of zeolite/fluid slurry used in the sealantmay vary depending on how much adsorbent capability is needed and on howmuch fluid is needed in the sealant.

The slurry of coated zeolite, in the amounts and prepared as describedabove, is combined with the sealant ingredients in a sigma blade mixerfor one hour and fifteen minutes. The temperature of the mix rises to260° F. as a result of internal friction. A vacuum of 25 inches ofmercury is applied during the last 20 minutes of the mixing process.Slugs of the resulting material are made, and are extruded into sealantstrips, incorporating an aluminum swiggle strip as described in U.S.Pat. No. 4,431,691. The sealant material in strip form is then coiledand sealed in cans.

Test samples of this sealant which incorporates the improved zeoliteadsorbent, and of a standard sealant, were pressed between glass andaluminum prior to conditioning at 135° F. and 100% relative humidity for24 hours. The sample of the standard sealant outgassed, forming bubblesat the interface between the glass and the sealant. The sealant of thepresent invention did not outgas or form any bubbles, and there was noloss of adhesion between the glass and the sealant.

It can be seen from the foregoing that the present invention provides animproved zeolite adsorbent having the desirable characteristics of (a) alack of gases such as nitrogen and oxygen, so as to minimize outgassingand re-adsorption of gases during periods of temperature or pressurefluctuation; (b) a lower capability to adsorb gases such as nitrogen andoxygen from air such as the air space in a double-paned glass windowbecause the pore apertures of the zeolite are covered with a layer offluid which is essentially impermeable to oxygen and nitrogen; and (c)an ability to slowly adsorb water vapor from the surrounding air andretain it in the pores of the zeolite, thus reducing condensation on theinner surfaces of the panes of glass in a double-paned glass window.

As used herein, term "outgas" or "outgassed" refers to zeolite which hasbeen heated to drive out gases and water vapor from the pores of thezeolite.

What is claimed is:
 1. An adsorbent useful in sealants for thefabrication of multiple glazed windows consisting essentially ofoutgassed zeolite having pores with apertures large enough to permitpassage of oxygen and nitrogen into the pore spaces and a layer of anorganic compound extending over said pore apertures, said organiccompound being essentially impermeable to oxygen and nitrogen andrelatively permeable to water vapor.
 2. An adsorbent comprising (i) azeolite having a surface and having a plurality of pores extendingthrough said surface into said zeolite, said pores having apertureslarge enough to permit passage of oxygen and nitrogen molecules throughsaid pore aperatures, and (ii) a fluid disposed on said surface of saidzeolite and extending over and covering said pore apertures, said fluidbeing essentially impermeable to nitrogen and oxygen molecules andrelatively permeable to water vapor; wherein said fluid is selected fromthe group consisting of paraffinic oil, naphthenic oil, and aromaticoil.
 3. An adsorbent as defined in claim 2 wherein the zeolite materialis a mixture of at least two zeolite materials having different poreaperture sizes.
 4. An adsorbent as defined in claim 3 wherein thezeolite is a mixture of a zeolite material having a pore aperturediameter of 4 angstroms with a zeolite material having a greater poreaperture diameter up to and including 10 angstroms.
 5. An adsorbent asdefined in one of claims 2, 3 or 4, wherein said fluid is a paraffinicoil.
 6. A sealant for multiple glazed windows having a zeolite adsorbenttherein, wherein said zeolite adsorbent, having pores with apertureslarge enough to permit passage of oxygen and nitrogen into the porespaces, is treated with a paraffinic, naphthenic or aromatic oil ormixtures thereof under heat or under heat and vacuum to render thezeolite permeable to water vapor and essentially impermeable to oxygenand nitrogen.
 7. A sealant as defined in claim 6 in the form of a slurryfurther comprising butyl, resin, zinc oxide, carbon black, aromaticresin and silane.
 8. A sealant as defined in one of claim 6 or 7 whereinsaid zeolite is treated with a paraffinic oil.
 9. A sealant as definedin one of claims 7 or 8 wherein the zeolite material is a mixture of azeolite having a pore aperture diameter of 4 angstroms with one or morezeolites having a pore aperture diameter greater than 4 angstroms and upto and including 10 angstroms.
 10. A sealant for multiple glazed windowshaving an adsorbent comprising (i) an outgassed zeolite having a surfaceand have a plurality of pores extending through said surface into saidzeolite, said pores having apertures large enough to permit passage ofoxygen and nitrogen molecules through said pore apertures, and (ii) afluid disposed on said surface of said zeolite and extending over andcovering said pore apertures, said fluid being essentially impermeableto nitrogen and oxygen molecules and relatively permeable to watervapor; wherein said fluid is selected from the group consisting ofparaffinic oil, naphthenic oil, and aromatic oil.
 11. A method of makinga zeolite adsorbent that is permeable to water vapor and essentiallyimpermeable to oxygen and nitrogen comprising the steps of:providing aparticulate material consisting essentially of zeolite having pores withapertures large enough to admit oxygen and nitrogen molecules into thepores; providing a fluid which is essentially impermeable to oxygen andnitrogen and which is relatively permeable to water vapor, said fluidbeing selected from the group consisting of a paraffinic oil, anaphthenic oil and an aromatic oil; mixing the zeolite material and thefluid to form a slurry of the zeolite and the fluid; heating the slurryto a temperature sufficient to substantially drive off nitrogen andoxygen from the zeolite; and cooling the slurry to room temperature. 12.The method of claim 13 wherein vacuum is applied while heating theslurry.
 13. The method as defined in one of claims 11 or 12 wherein saidfluid 15 is paraffinic oil.
 14. The method as defined in one of claims11, 12 or 13 further comprising the steps of:mixing the cooled slurrywith butyl, hydrocarbon resin, zinc oxide, carbon black, aromatic resin,and silane; heating the mixture at least partially under vacuum; coolingthe mixture; and forming the mixture into strips suitable for use as asealant material for multiple glazed windows.
 15. A sealant strip formultiple glazed windows prepared according to the method of claim 14.